Finite Element Analysis, Experimental Compliance Monitoring And Clinical Application Of New Modified Three-dimensional Thoracolumbar-sacral Orthosis

【Background】Adolescent idiopathic scoliosis(AIS) is one kind of three dimensional spinaldeformity,involving the coronal, sagittal and axial planes,which is frequently seenduring the period of puberty.It is reported that the prevalence rate is about1-3%.Theetiology of this disease remains unclear, although there are many assumptions.So it’sdifficult for us to etiologically treat it successfully. If the patients don’t recieve righttreatment in time, the spinal deformity will inevitably deteriorate,which results inworse appearance, cardiopulmonary function and mental health, accompanying withsevere economic and social problems. For patients with severe spinal deformity andCobb Angle more than45°, they usually need surgical treatment. For patiens withbone immaturity and Cobb Angle between25°~40°, brace treatment is consideredto be the only effective way. However,there are some shortcomings of bracetreatement for AIS, One is that brace compliance (wearing time and effectiveinterface force) is often impossible to monitor.In the past most of the studies,thecompliance was subjectively evaluated.Until recently,some authors begin to usetemperature or humidity sensor to monitor wearing time without trunk pressureapplied by the brace.Another disadvantage, traditional Boston othorsis works mainlythrough imposing pressure on the three or four points of the trunk to achieve the goalof preventing the progress of spinal deformity, but it often leads to sagittal flat backphenomenon clinically, decreasing the patient’s respiratory function.It is unable tocorrect the deformity three-dimensionally. Some researchers found Scolioticdeformities are significantly reduced in supine position by a lordotic fulcrum force onthe thoracolumbar junction. Conservative treatment using the new brace inscoliotic and kyphotic deformities demonstrates a marked improvement after one yearalso in clinical and postural criteria. The new brace is modified from the30olordosis Boston Brace.No asymmetric pressure on bony structures was used, but extrapadding was placed at the thoracolumbar spine at the paravertebral mass of themusculus erector trunci to create a lordotic fulcrum inside the brace. Therefore, thisstudy group put forward a new type of three-dimensional corrective orthosis on thebasis of theoretical research before.We modified Boston brace by building15°lordosis at the thoracolumbar segment and placing a airbag inside to adjust thepressure.In this way can it maintain the coronal load and sagittal pressure at the same time. No similar report has ever been seen.The finite element method is used tobuild the complete scoliosis model, including belly wall,thoracic cage,brace and soon.Then,simulation study is performed to compare the results after the application oftraditional and new braces based on the model.In the end,this new type ofthree-dimensional corrective brace can be used in the clinic,which has been littlereported so far.【Objectives】Computer aided technologies were used to establish finite element models basedon the patient’s CT scan image,including verterbras,discs,the nucleuspulpusos,ligaments,throcic cage and so on.After parameters optimization andvalidation,the finite element model was used to simulate brace treatment by placingpressure on the sagittal thoracolumbar junction by the new brace to get much bettercorrection and sagittal alignment.After the simulation,this new type ofthree-dimensional brace is applied in the clinic to confirm its better immediatecorrective outcome than traditional Boston brace. Moreover, a set of cable andwireless compliance monitoring equipment is established to record the wearing timeand interface pressure to improve the outcome of brace treatment.【Methods】1. Establishment,validation of the3-D finite element model of AIS andsimulation of new brace treatmentA14-year-old female patient with scoliosis was chosen to accept thin CT scanfrom C7to pelvic. For CT images were imported to software Mimics10.0to establishfinite element model.After the geometric cleaning, the model was imported tosoftware Ansys11.0for the division of grid, definition of nodes connection andattachment of material properties.Then,the intervertebral disc, rib cartilage, sternumbone, ligament, abdominal wall,orthorsis and so on were added.A complete AISmodel was finished and validated.Based on this model,simulation of different bracetreatment was performed to observe the change of the spinal parameters and tocompare the treatment outcome.2. Development of a compliance monitoring system Pressure sensors were used to measure the interface pressure between brace andtrunk body.The microprocessor collected data and calculated,then transmitted theresults to the PC through USB.A self-developed program was applied to read thepressure value and set a certain threshold.When the pressure was above thethreshold,it was deemed to be effective and the action time wascumulated.Otherwise,when the pressure was below the threshold,it would be warnedwith the alarm sound. Wireless monitoring system was bulid via bluetoothmodule.The signal can be reached by the apple smartphone and read by the Appsoftware.3. Biomechanical analysis and clinical application of the new3D correctivebrace.Nineteen patients with AIS were included to wear the traditional Boston braceand the new brace.The maximum tightness was close to the threshold that patients cannot tolerate and the interface pressure was then measured at the the fivepoints,including right thoracic,left axil,left lumbar,and bilateral iliac crest. Pressuredata were recorded by I-scan system and spinal parameters were observed by takingwhole spine X-rays. Keeping the coronal pressure consistent, a new type ofthree-dimensional brace was worn to give80N force at the thoracalumbar area.Thespinal parameters were also recorded to compare the outcome between two differentbraces.【Results】1. The3-dimensional finite element model of AIS was established successfully,including all the spine vertebraes,thoracic cage,clavicles, capulas,ligaments,discs,nucleus pulposus,belly and brace. The model was validated to have good geometricsimilarity with X-ray. The standard strap tensions (40N) were loaded on the back ofthe brace to simulate the coronal pressure of the traditional brace. It showed thoracicand lumbar curve decreased7°and6°respectively.We also found that thoracickyphosis and lumbar lordosis reduced2°and3°respectively.To keep the straptension unchanged, different loads (40N,60N,80N)were put at the thoracalumbar segment,we found that lumbar lordosis increased obviously and thoracic kyphosisincreased slightly,while thoracolumbar kyphosis decreased obviously. Even more,therotation of the apical vertebra and coronal spinal curve decreased more.The spinalparameters changed most after the application of the80N at the thoracolumbarsegment.Thoracic kyphosis and lumbar lordosis increased2°and7°, respectively.Coronal thoracic and lumbar curve reduced9°and13°, respectively.2.A cable and wireless monitoring system was successfully established.After thatpressure sensor collected the data, microprocessor can accept and calculate these datafrom pressure sensor,then transmit these data to PC through USB.A programme basedon visual studio was developed by our group to read and display these data on the PCscreen. When the pressure was above the threshold setted by the programme,theeffective action time was cumulated.Otherwise,it would be warned with the alarmsound. On this basis of the previous research, we used redbear BLE shields withbluetooth4.0module to connect the Arduino panel.Then,the pressure data can betransmitted to iPhone5S. App software Lightblue was used to read and record it.3. I-scan system was applied to measure the interface pressure at the five pointsafter traditional Boston brace treatment,including right thoracic force with61.8±17.9N,left axil with21.0±6.9N,left lumbar with31.1±11.4N,right pelvic with29.5±11.9N,left pelvic with25.4±11.1N.But forces at these five points were62.4±17.1N,21.8±7.1N,31.1±10.8N,29.1±12.3N,24.8±9.8N respectively after thenew brace treatment.There were no statistical differences between them（P>0.05）.Thoracolumbar lordotic force was78.3±6.1N.After traditional brace treatment,correction rate of thoracic and lumbarcurve,thoracic and lumbar apical verterbrae rotation were21%,31%,13%,36%respectively,while they were36%,52%,39%,53%respectively after new bracetreatment.It showed that these two kinds of braces were statistically effective（P<0.01）,even it could get much better outcome with new brace treatment.For thesagittal alignment,it could decrease thoracic kyphosis and lumbar lordorsissignificantly（P<0.05）with traditional brace,while it could increase lumbar lordorsis with statistical significance （P<0.05） and increase thoracic kyphosis withoutstatistical significance(P>0.05)with new brace.To analyze the correlations between the forces of five points and corrective rateby using bivariate correlation analysis, we found that the right thoracic force and leftaxillary force were related to the orrection rate of thoracic rotation after traditionalbrace treatment, and left axillary force was related to the correction rate of thoraciccoronal angle(P <0.05). There were no correlation between the force of other pointsand correction rate.【Conclusions】1.A AIS finite element model has been successful established and validated.Basedon the simulation study, the new type of3D corrective brace can get better coronalcorrection rate,higher thoracic kyhposis and lumbar lordosis than traditionalbrace.Moreover,the spinal parameters including coronal,sagittal and axialalignment,can be best restored after the application of the80N at thoracolumbarregion.It is helpful for the next clinical study.2. A cable and wireless monitoring system has been successfullyestablished,which is helpful to develop wearable device in the future.3.The interface pressure at the five points after traditional Boston brace and new3D corrective brace treatment has been measured by I-scan system.The force at theapical vertebra of right thoracic and left lumbar help most for the correction,while theother force provide minor support for the deformity correction.4. For different patients, there are no obvious correlation between force generatedby the brace and the correction rate.It shows that there are some other factors involvedworking for the deformity correction.5. With the new type of three-dimensional corrective brace can provide force notonly on the coronal plane but also on the sagittal thoracolumbar region,resulting inbetter deformity correction in the three planes than traditional Boston brace,avoidingthe flatback phenomenon.